The deal is done, per The Sun:
The contract will pay Walker, arguably the best left-handed reliever on the free agent market, approximately $11.5 million over three seasons. The deal will not be official until Walker, who had a 2.81 ERA in 56 games last season, takes and passes a physical.
UPDATE, 3:38pm EST Thursday:
Sportline is reporting that it's $12M.
Left-hander Jamie Walker and the Baltimore Orioles reached a preliminary agreement on a $12 million, three-year contract.
Walker will get $3 million next year and $4.5 million in each of the following two seasons. The deal is subject to a physical, scheduled for Friday.